This invention relates to making surgical instruments, in particular surgical instruments in which an inner tube that carries a cutting implement is disposed for movement within an outer tube having a cutting window that exposes the cutting implement to tissue.
The inner and outer tubes of such surgical instruments typically have closed distal ends, and the cutting implement and window are formed at or near the distal ends. The cutting implement is often an opening with sharpened edges, in which case the edges of the window may also be sharpened. In some cases, the cutting implement and window are formed in the closed distal ends themselves.
The tubes are typically made from two piecesxe2x80x94a metal tube open at both ends and a hollow, drawn metal tip which is open at one end and closed at the other. The open end of the tip is attached to one end (e.g., the distal end) of the tube, such as by plasma arc welding. The weld joint is smoothed by, e.g., centerless grinding.
One scheme for making the tube from one piece is known as xe2x80x9cspinning.xe2x80x9d In this process, the open distal end of the tube is cut off at a shallow angle to produce an elongated, generally side-facing opening. The tube and a supporting mandrel are then spun at high speeds and advanced into a die. The friction between the tubs and the die heats the tube to a plastic state so that the die forces the material surrounding the opening to one side. This forms a rounded, closed end at the distal tip of the tube, and a side-facing opening located proximally of the tip.
This invention features making a one-piece inner or outer tube for a surgical instrument by swaging the open end of the tube closed. Among other advantages, closing the tube by swaging reduces manufacturing complexity. For example, swaging eliminates several steps associated with the two-piece attachment process (e.g., straightening the two-piece tube and grinding smoothing the joint between the tip and the tube). Additionally, there is no need to cut an elongated opening in the tube, as in the spinning process.
In one general aspect of the invention, a tubular member that is to serve as either the inner tube or the outer tube is provided, and an open distal end of the tubular member is swaged closed.
Preferred embodiments may include one or more of the following features.
The swaging is performed by rotary swaging. The tubular member includes a distal edge that defines an opening at the distal end, the swaging driving regions of the tubular member disposed adjacent to the distal edge together to close the opening. Prior to swaging, the distal edge is disposed symmetrically about, and perpendicular to, an axis of the tubular member, and the swaging drives the adjacent regions of the tubular member together symmetrically with respect to the axis.
The swaging produces a seam in material of the tubular member at the distal end, and this material is fused together at the seam. Preferably, the fusion is performed by welding the distal end.
The swaging also produces a protrusion of the tubular member material at the seam. Prior to welding, a selected amount of the protrusion is cut away. Performing this step helps control the final tube length as well as the wall thickness at the distal end.
The closed distal end of the tubular member is formed into a selected shape. Preferably, this is done by pressing the distal end of the tube between a pair of dies that define the selected shape.
In one embodiment, the selected shape is rounded so that the distal end defines convex (e.g., substantially hemispherical) interior and exterior distal surfaces. This renders the tube suitable for use in full-radius surgical instruments. In another embodiment, the selected shape is flattened so that the distal end defines flattened interior and exterior distal surfaces. In this case, the tube can be used in end cutting surgical instruments.
The tubular member may be provided as the inner tube of the surgical instrument, in which case, a cutting implement is disposed at the distal end of the tubular member. The tubular member is disposed for rotation within the outer tube of the surgical instrument.
The tubular member may be provided as the outer tube of the surgical instrument, in which case a window is defined at the distal end for exposing a cutting implement carried by the inner tube.
A second tubular member may be provided to serve as the other one of the inner tube or the outer tube. Swaging is performed to close the open distal end of the second tubular member.
Another general aspect of the invention features performing some or all of the actions discussed above to make a tube for use as an inner or outer tube of the surgical instrument. That is, swaging is performed to close the open distal end of the tubular member, a selected amount of a protrusion formed by the swaging is cut away, the tube material is fused together at a seam formed by the swaging, and the closed distal end of the tubular member is formed into a selected shape.
In another aspect of the invention, the swaging, cutting, fusing, and forming operations are performed at various stations. In a preferred embodiment, devices convey the tubular member between the stations, and a controller controls the conveying and coordinates operation of the stations.
The invention provides one-piece tubes with precisely sized and shaped closed distal ends within tight tolerances. This allows the inner and outer tubes to be designed to have small clearances between them for increased cutting efficiency. In addition, the one-piece construction is stiffer than typical two-piece tubes, because there is no weld joint that requires smoothing by centerless grinding or the like. The high degree of stiffness maintains the close running fit around the entire circumference of the tubes"" distal ends and at the extreme distal tips of the tubes, even if the tubes are subjected to large side loads during use.
Other features and advantages of the invention will be apparent from the following description, and from the claims.